We investigated the influence of body size on rarity patterns at a regional scale
using the tenebrionid beetles of Latium (Central Italy). For this we calculated geographical
range size (no. of 10 km square cells), habitat breadth (no. of phytoclimatic units), and
abundance (no. of sampled individuals) using a large database containing 3,561 georeferenced
records for 84 native species. For each species, we used total body length to
correct rarity measures for body size. Then we calculated vulnerability (Kattan) indices
using both corrected and uncorrected rarity scores. Finally we used species range trends
(expanded vs. contracted) as a measure of actual species decline. We found that range
trends were correlated with vulnerability index independently from body size correction,
the species with the highest vulnerability being those that experienced the strongest range
contraction for both corrected and uncorrected measures. Also, we found that correcting
for body size may be problematic because of the weak correlations between body size and
geographical and ecological rarity (notably, abundance was not correlated). These findings
indicate that correcting rarity for body size is not only theoretically questionable, but also
practically difficult and possibly useless for conservation purposes.

We investigated the influence of body size on rarity patterns at a regional scale
using the tenebrionid beetles of Latium (Central Italy). For this we calculated geographical
range size (no. of 10 km square cells), habitat breadth (no. of phytoclimatic units), and
abundance (no. of sampled individuals) using a large database containing 3,561 georeferenced
records for 84 native species. For each species, we used total body length to
correct rarity measures for body size. Then we calculated vulnerability (Kattan) indices
using both corrected and uncorrected rarity scores. Finally we used species range trends
(expanded vs. contracted) as a measure of actual species decline. We found that range
trends were correlated with vulnerability index independently from body size correction,
the species with the highest vulnerability being those that experienced the strongest range
contraction for both corrected and uncorrected measures. Also, we found that correcting
for body size may be problematic because of the weak correlations between body size and
geographical and ecological rarity (notably, abundance was not correlated). These findings
indicate that correcting rarity for body size is not only theoretically questionable, but also
practically difficult and possibly useless for conservation purposes.